History of Audio Technology
'History of Development of Audio Technologies' The text below outlines some of the key milestones in Audio technology, focusing specifically on the technology in relation to the spatial information it is able to replicate. Early sound reproducing technology began in the late 1800s and the early 1900’s with the invention of the first gramophone and phonograph recording system, which were initially monographic, (one channel audio). The only ‘spatial’ cues possible in monophonic reproduction were hints at distance and depth provided by reverberation. Another key milestone in the early stages of audio technology was Clement Ader’s early experiment at the Paris exhibition of 1881, which is often documented as the first known example of stereophonic transmission. Ader was able to achieve this by placing telephone pickups (microphones) in the footlights at the Paris Opera (spaced across the stage) and relayed the outputs of these to pairs of telephone receiver earpieces at the exhibition, where delighted visitors could listen to the opera live and with some spatial realism. Unfortunately it was not until many years afterwards that stereophonic reproduction became a commercial reality. A key milestone in audio technology also came in 1930 with early work on directional reproduction at Bell labs, which involved attempts to approximate the sound wavefront that would result from an infinite number of microphone/ loudspeaker channels by using a smaller number of channels. By March 1930 the BBC had opened a second radio transmitter, and so simultaneous sound and picture transmissions began. 1931 was a key year for audio technology with the Blumlein patent, which was created by Alan Blumlein which allowed for the conversion of signals from spaced pressure microphones which generated phase differences relating to the position of the source, to a format suitable for reproduction on loudspeakers. Blumleins' work showed that introducing amplitude differences between a pair of loudspeakers, it was possible to create phase differences between the ears. The patent itself left the blueprint for stereo-pair microphone techniques. Blumleins work remained unimplimented in commercial products, and it appears that his work was overlooked in much publications about stereo reproduction, even up until the 1950’s. In 1958 Blumlein’s theories were revived in a paper by Clark, Dutton and Vanderlyn of EMI. The paper showed in more rigorous detail how a two loudspeaker system could be used to create an accurate relationship between the original position of a source and the perceived position in reproduction, by controlling the signal amplitudes between loudspeakers, which were derived from a pair of coincident figure-eight microphone. The authors discussed the three channel spaced microphone system of Bells Labs and suggest that although it produces convincing results, it is was deemed uneconomical for domestic use, and that a two channel specification (which was a simplified specification using two spaced microphone about 10 feet apart), there was a perceptual “hole in the middle” effect in which sound seems to appear from either left or right, without a clear centre image. They concluded Blumleins method didn't take advantage of the principles of binaural hearing. In the 1950’s Blumleins' theories also made way for two channel stereo sounds to be cut on vinyl. In 1960 FM radio was broadcast with a superior quality of audio the majority of consumers had never heard before. On the 28th August 1962, experimental stereo radio broadcasts begin. Up until the 1980s Television relied upon frequency modulated systems in order to deliver video and audio signals simultaneously to consumers households. In the early 1980‘s a system called NICAM was invented by the BBC Research Centre, Kingswood Warren. It was first applied to the British "System I" 625 line PAL colour TV broadcasting system, and premiered in 1986 on the "First Night of the Proms" concert programme. NICAM offered a totally different approach to Television audio broadcasting, providing a completely new all-digital stereo/twin-mono service in addition to the one provided by the existing FM sound. Theoretically, a NICAM equipped TV service could offer 3-language support: the FM sound plus NICAM (in twin-mono mode) all carrying different services. Another area of research in audio technology has been into Binaural stereo. Binaural stereo is a term used to describe signals that have been recorded or processed to represent the amplitude and spatial timing characteristics of a sound as it is received by human ears. There are various methods of recording stereo sound, but in order to capture binaural audio, two microphones are located in the ears of a dummy head, which allows sound to be encoded with all of the spatial cues received by human listeners. Unfortunately this technology is prone to localisation errors that derive from, differences between the recording head/ears and the listener’s, the headphone response and coupling to the ears, and any distortions in the signal path, can easily destroy the subtle spectral and timing cues required for success. Recent developments in digital signal processing in the 1990‘s have resulted in a resurgence of interest in binaural technology. Often being referred to as ‘3D audio’ and ‘virtual surround’, it is now possible to process multiple tracks of audio to mix sources and pan them binaurally. Binaural audio can easily be processed for reproduction on loudspeakers, and one application being investigated is use in consumer televisions for spatial enhancement of the sound from only two loudspeakers. It is nonetheless important to highlight that the system only work satisfactorily for a very limited range of listening positions. Multi-channel audio was something that initially evolved through cinema technology, although in cinema, sound did not incorporate stereo reproduction until the 1950s. Stereo film sound tracks was considered a laborious and time consuming process and so this technique gradually died out in favour of dialogue being centred, with stereo music and sound effects panned. Multichannel stereo formats for the cinema became increasingly popular in the late ’50s and 1960s, with the advent of the 70 mm format which involved multiple front channels, a surround channel as well as a subwoofer channel to accompany high quality, wide-screen cinema productions. In the early 1970s, Dolby’s “Dolby Stereo” was announced which enabled a four channel surround sound signal to be matrix encoded into two optical sound tracks recorded on the same 35 mm film as the picture. This is still the basis of the majority of analogue matrix film sound tracks today, having been released in a consumer form called Dolby Surround for home cinema applications. The 1970’s seemed to be a great era in terms of audio innovation, particularly in multichannel audio formats. Arguably one of the biggest innovations was Ambisonic’s. Ambisonic sound was developed in the 1970’s, and is a comprehensive approach to the reproduction of directional sound, using theoretically an infinite number of reproduction channels, based on a extension on the Blumlein principle. The ambisonics system is flexible and can be adapted for a wide variety of loudspeaker arrangements, such as stereo or 5.1channel configuration. One of the key innovations in ambisonics is that it enables three dimensional sound fields, (including height information) to be represented in an efficient form that allows accurate localisation when the spatial audio is reproduced. Despite the brilliance of ambisonic technology, the technology unfortunately did not gain commercial acceptance. The lack of commercial success could be because the ambisonics states a collection of principles and signal representation as opposed to a method of implementation. In recent years, the development of new consumer audio format ITU 5.1 has been introduced. ITU 5.1 was invented in 1976, and is the common name for the six channel ‘surround sound’ multichannel audio systems which concept of the home cinema has apparently captured the consumer imagination, leading to widespread installation of surround sound equipment in domestic environments. Most Recent digital formats typically conform to the ITU 5.1-channel configuration (three front channels, two surround channels and an optional sub-bass effects channel that is known as the ‘0.1’), in which the front left and right channels retain compatibility with two channel stereo. ITU standard does not define anything about the way that sound signals are represented or coded for surround sound, it simply states the layout of the loudspeakers. On the 3rd April 2010, BSkyB launched its “Sky 3D” which is a television channel on the Sky platform, that launched on 3 April 2010 with the Manchester United vs Chelsea football match being broadcast in over a thousand pubs across the UK and Ireland in 3D. Sky’s preferred audio format for 3D was 5.1 surround format, as with its 2D coverage.